An X-wing aircraft is a rotary wing aircraft that uses a rigid rotor/wing utilizing circulation control airfoils. The rotor is driven mechanically and the rotor blades operate essentially in fixed pitch. The rotor may rotate, as in a helicopter, or it may be stopped and positioned so as to act like a fixed wing. Collective and cyclic control is achieved by control of air circulation about a Coanda surface on the blade airfoils. This is done by blowing compressed air through leading edge and trailing edge duct in the rotor blades and modulating the amount of air being ejected through spanwise slots on the leading and trailing edges of the rotor blades.
The rotor system for an X-wing aircraft includes a hub and attached rotor blades and a pneumatic system for delivering pressurized air separately to the leading edge and the trailing edge of the individual rotor blades at a desired pressure and mass flow. The pneumatic system includes a compressor, a stationary air supply chamber, valving for controlling the flow of air from the chamber to the blades, and a rotating air distribution arrangement for conducting air separately to the leading edge and trailing edge of the blades.
In circulation control airfoils, pressurized air is ejected from spanwise openings or slots along the upper side of the rounded airfoil leading/trailing edge Coanda surface. The airflow from the slots attaches to the rounded leading/trailing edge which increases the circulation to provide a corresponding lift increase over an airfoil having no ejected air. While the discussion throughout this description pertains to and describes slots located in the upper surface of blades to provide upward lift, it should be recognized that a slot may be desired on the blade lower surface for lift control. For a given blade internal pressure and aerodynamic condition, the lift change due to circulation control is proportional to the area of the slot opening up to a certain limit. When the slot opening exceeds this limit no additional lift is achieved, a condition analogous to stall in a conventional airfoil. Since an X-wing circulation control airfoil is symmetrical about its half chord, the leading edge on the advancing side of the blade path disc becomes the trailing edge on the retreating side, and vice-versa. To maximize performance as the rotor slows down, it is desirable that the "local" leading edge slot be closed at all azimuth positions. The use of conventional preload springs for closing the slot is not desirable primarily because of the weight which would be involved.
A rotor blade construction having adjustable spanwise slot openings is described in U.S. application Ser. No. 664,738 which issued Dec. 2, 1986 as U.S. Pat. No. 4,626,171. This construction is an alternative configuration which resulted from scale model testing of the patented construction and which offers possible load, weight and stress benefits.
Davidson et al U.S. Pat. No. 3,139,936 describes a helicopter control mechanism, Cheeseman et al U.S. Pat. No. 3,524,711 describes a helicopter rotor blade having spanwise extending slots, and Cheeseman et al U.S. Pat. No. 3,554,664, Linck U.S. Pat. No. 3,873,233 and Grant et al U.S. Pat. No. 4,137,008 describe circulation control airfoils.
A circulation control rotor system is described in the report titled "Circulation Control Rotor Flight Demonstrator" by David R. Barnes, Douglas G. Kirkpatrick and George A. McCoubrey presented at an American Helicopter Society Mideast Region Symposium in August, 1976. The report titled "Status Report on Advanced Development Program Utilizing Circulation Control Rotor Technology" by Kenneth R. Reader, Douglas G. Kirkpatrick and Robert M. Williams, Paper No. 44 presented at the Fourth European Rotorcraft and Powered Lift Aircraft Forum, Stresa, Italy, Sept. 13-15, 1978 describes an X-wing development program.